Centrifugal wind classifiers



Jan. 26, 1960 K. A. G. GUSTAVSSON ET AL 2,922,520

CENTRIFUGAL WIND CLASSIFIERS 3 Sheets-Sheet 2 Filed March 4, 1958 K424,4XEL GoZe/W Gqsm VS'SON .60 Gusnfl/ 514/4 M4A/ss0/v INVENTORS Jan. 26,1960 s vss N ETAL 2,922,520

CENTRIFUGAL WIND CLASSIFIERS Filed March 4, 1958 5 Sheets-Sheet 3 KARLAXEL Ede/w Gqsmvssou 50 GUSTAV fM/L MANSSOA/ INVENTORS zum,aa, $44. 4.,m

ATTORNEYS CENTRIFUGAL WmD CLASSIFIERS Karl Axel Giiran Gustavsson and BoGustav Emil Mansson, Enkoping, Sweden, assignors to Aktiebolaget Bahco,Stockholm, Sweden, a corporation of Sweden Application March 4, 1958,Serial No. 719,076

Claims priority, application Sweden March 8, 195 7 4 Claims. (Cl.209-144) The present invention relates to a centrifugal wind classifierfor separating or fractionating granular or pulverulent material. Themain object of the invention is to arrange a centrifugal wind classifierso that a sharp fractionation limit can be achieved for all types ofmaterial which are to be treated in the classifier with regard to thespecial characteristics of the materials, as well as to achieve the mosteflicient possible utilization of the classifier.

The invention relates to a centrifugal wind classifier of the type inwhich the material to be classified is introduced into a stationaryseparation chamber as an evenly distributed annular curtain and isseparated in the separating chamber into a coarse and a fine fraction bymeans of a gas current which is introduced into a space surrounding theseparating chamber through a tangentially directed gas inlet and isthereby imparted a rotary motion and then enters the separating chamberaround the circumference thereof and finally leaves at the center of theseparating chamber. The above-mentioned main object of this invention isachieved thereby that the width of the tangential gas inlet and theheight of the separating chamber are adjustable whereby it is possibleto vary both the tangential and the radial velocity components of thegas current flowing through the separating chamber.

In a preferred embodiment of the invention, the separating chambercontains a rotatable plate provided with blades, said plate beingmounted to rotate in a plane substantially perpendicular to the annularcurtain of material and to impart to the material a tangential velocitycomponent substantially corresponding to the tan gential velocitycomponent of the gas current when the width of the tangential air inletis adjusted to a middle position. Thereby, the material to be classifiedwill be imparted an initial tangential velocity component which normallyis close to that which it is to be imparted by the gas current so thatthe work which the gas current has to perform to impart to the materialthe desired tangential velocity will correspond only to a minoracceleration or, possibly, deceleration of the material. Thereby, thefiactionation efliciency of the apparatus will be improved.

The invention will be described more in detail below with reference tothe accompanying drawings which show two embodiments serving toillustrate but not to limit the invention.

Figure 1 shows one embodiment in cross-section. V

Figure 2 shows a horizontal cross-section along line IIII in Figure 1.

Figure 3 is a vertical central cross-section similar to Figure 1 butillustrating a second embodiment.

Referring to Figures 1 and 2, the centrifugal wind classifier comprisesa substantially cylindrical casing 1 formed integral with atangentially-directed air inlet 2, and a conical bottom part 3 attachedto the casing 1, the part 3 forming a hopper for collecting the coarsevertical central "ice material separated and having an outlet 4 fordischarging the coarse material. A central air outlet 5 is disposedadjacent the center of the upper portion of the bottom part 3 andcommunicates through a conduit 6 which passes through the wall of thebottom part 3 with a conduit 7 which leads to a fan (not shown) and isprovided with a damper 8 by means of which the rate of air flow can beregulated.

Affixed around the circumference of the air outlet 5 is a conicalannulus 9 which forms the lower wall of the separating chamber.Upwardly, the separating chamber is defined by the bottom wall of aconical material distributor 10 and by a frustoconical flange 11attached to a-conical jacket 12 surrounding the material vdistributor10. The jacket 12 is attached'to a cylinder 13 which extends upwardlythrough a central opening in a roof 14 which closes the top of theclassifier. The material distributor 10 is attached to a rod15'concentric with the cylinder 13. The upper portion of the rod 15 isthreaded and carries a nut 16 which rests on a yoke 17 attached to thecylinder 13. By tightening the nut 16, the jacket 12 can be caused toengage a number of spacer members 18 attached around the materialdistributor 10, which spacer members determine the, width of theclearance between the material distributor l0 and the jacket 12. Theupper threaded part of the rod 15 also carries a handwheel 19, whichrests on a yoke 20 carried by the roof 14. By means of this handwheelthe assembly comprising the material distributor 10, the cylinder 13 andthe jacket 12 with associated parts can be lifted or lowered, so as tovary the height of the separating chamber.

Disposed in the cylinder 13 and surrounding the rod 15 is a materialfeeding funnel 21 which is veltically displaceable. Around its uppercircumference the funnel 21 has a number of bolts 22, which projectthrough slots 23 in the cylinder 13 and which carry nuts 24, by means ofwhich the funnel can be fixed in the desired position.

The tangential air inlet 2 can. be partly or wholly closed by a damperconsisting of a substantially semicircular plate 25 which is adapted toslide in guiding channels 26.

In operation, the material to be classified is fed through the funnel 21and slides along the conical outer surface of the material distributor10 at a rate determined by the clearance between the top end of thematerial distributor l0 and the lower end of the funnel 21, whichclearance is adjusted by positioning the funnel 21 as explained above.Thereupon, the material falls into the separating chamber as an annularcurtain through the clearance between the material distributor 10 andthe jacket 12. Air enters through the inlet 2 and is given a rotatingmotion within the casing 1. During continued rotation the air thenenters the separating chamber from which it flows through the outlet 5.The material to be classified is carried along in the rotating movementof the airin the separating chamber. The fine material is carried by theair current towards the center of the separating chamber and may berecovered from the air flowing away through the conduit 7, while thecoarse material is thrown out toward the circumference of the separatingchamber by the centrifugal force to fall down into the lower part 3 ofthe classifier from which it may be discharged through the opening 4.The tangential velocity component of the air in the separating chamberis adjusted by closing the air inlet to a desired extent by means of thedamper 25, while its radial velocity component is determined by theheight of the separating chamber which is adjusted as above explained.By this combined possibility of adjustment a very sharp fractionatinglimit .may be set within wide limits of particle sizes, and at the sametime-both the radial and the tangential velocity components may bevaried within wide ranges, whereby it will be possible to adjust theconditions in the separating chamber to suit the characterHof thematerial treated and also to utilize the classifier in the mostefficient way possible for the material in question. This will beunderstood from the following explanation.

Aparticle in the separating chamber is subjected to the actions of twooppositely directed forces. One of them is directed radially outwardlyand is a function of the tangential velocity of the gas, the radius ofrotation and the diameter and specific gravity of the, particle. Theother force is directed radially inwardly and results from the frictionof the gas on the particle surface. It is a function of the radialvelocity of flow of the gas, "the particle diameter, the specific weightof the gas and a coefiicicnt of resistance which in its turn is afunction or Reynolds number and of the cinematic viscosity of the gas.The two forces can be expressed by the following equations:

Where C =the force directed radially outwardly D=the particle diameter q,,=the specific gravity of the particle V =the tangential gas velocityR=the radius of rotation (radius of the separating chamber) F =the forcedirected radially outwardly 'y =the specific gravity of the gas V '=theradial gas velocity C,,=a coetficient of resistance g=the gravitationconstant For a given rate of 'gas flow, V, is a function of the gasinlet width and V is a function of the height of the separation chamber.

If C=F D can be solved, provided that the values of the other variablesare known. A particle having a diai'neter D determined in this way willbe in equilibrium (i.e. it will rotate without moving eitherinwardly oroutwardly), while larger particles are thrown outwardly and finerparticles are carried along inwardly by the gas current. Thus, thisdiameter D is the fractionation limit under the conditions prevailing inthe separating chamber.

From a study of the above equations it will be seen that for a certainparticle in equilibrium (a certain fractionation limit) an arbitraryvalue for V, or V can be selected and a corresponding V or V;,respectively, can be calculated. Thus, if a certain separating chamberheight has been selected, a gas inlet width correspending thereto can becalculated and adjusted. On the other hand, if a certain inlet width hasbeen selected, a corresponding separating chamber height can becalculated and set.

It is seen from the above, that if the height of the separating chamberis invariable, a predetermined fractionation limit may be obtained onlywith a definite value for thetangential air velocity (width of airinlet). On the other hand, if the width of the air inlet is in variable,a predetermined desired fractionation limit can be obtainedonly with adefinite radial air velocity (height of separating chamber). In both ofthese cases therefore,-tl1e classification operation'is restricted to adefinite'value for both-the tangential and the radial gas'velocity'components to obtain a certain desired fractionation-limit.In-contrast, if according to the present invention both the width of thegas inletand the height of the separating chamber can be varied, thedesired fractionation limit can be obtained within wide ranges of bothradial and tangential air velocities provided that these two variablesare adjusted to each other in accordance with the equations above. Thismeans that it is possible to select either the radial air velocity orthe tangential air velocity freely in a manner such that it is suitablefor the material to be treated and thereupon adjust the tangentialvelocity or the radial velocity respectively so that the desiredfractionation limit is obtained. Thus, e.g., for some types of material,it may be suitable to subject the material to an intense centrifugalfield. In such a case a high tangential air velocity will be selected,whereupon a high radial air velocity corresponding to the tangentialvelocity and to the desired fractionation limit is determined.Furthermore, for some types of material it may be desirable to work witha great height of the separating chamber (if the material to beclassified is voluminous). In such a case the fractionation limit may beobtained by adjusting the air inlet width to a corresponding value.

It appears from the above considerations, that the .combination of thisinvention permits a sharp adjustment of a desired fractionation limitwith simultaneous regard to the character of the material treated in amanner which is impossible to achieve it only the tangential airvelocity or only the radial air velocity is variable. Furthermore, foreach material it is possible to select the conditions such that theapparatus is utilized as efficiently as possible for the material byselecting the highest possible air velocities which can be withstood .bythe material.

The. embodiment of Figure 3 is substantially similar to that describedabove with reference to Figures 1 and 2, and the parts which are similarhave the same reference characters. These parts need not be describedanew.

In this embodiment'the lower defining Wall of the separating chamber,which is denoted 91, is plane instead of conical and similarly, theflange 1 1 of the jacket 12 is plane. Furthermore, an electric motor 27is arranged within the air distributor 10 and is carried by a suppo'rt28 disposed within the air distributor. On the motor shaft 29 thereisattached a disc.30 provided with blades 31. These blades will impart tothe material falling down between'the distributor 14) and the jacket '12a tangential component of velocity which is substantially equal to thetangential component of velocity of the air current when the damper 25is in a middle position. Thereby, the fractionation elficiency willfbeimproved, as explained hereinbefore. In this embodiment,.thematerialdistributor is rigidly secured to the jacket 12 by means of the spacers18,, which. in this .case are. tubular. Through them air will beaspirated by theablades-31 to. cool the motor 27. Otherwise, thefunction of this embodiment is in every respect similar to that whichhas been described above with reference to Figures 1 and .2.

While specific embodiments and details have been shown and described,the invention is not limited to them,

since many modifications and variations obvious to those skilled in theart are possible without departing from the spirit and scope of thisinvention.

We claim:

l. A centrifugal wind classifier comprising a verticalsubstantiallycylindricalcasing, two substantially horizontal Wallsdisposed in said casing concentric therewith and spaced therefrom todefine a separating chamber within saidcasing, a tangential gas inlettangentially intersecting said casing, a central gas outlet in one ofsaid horizontal walls, whereby a gasintroduced into said casing throughsaid tangential inlet has imparted to itza rotating move- :ment andpasses through .said separating chamber and out through said central voutlet,-means;for feeding material'to 'beyclassified as an evenlydistributed annular curtaininto saidseparating chamber :adjacent itscircumference to cause-separation of :said material into coarse and-finefractions by said gascurrentymeans for varying -;:-th e:height OfcSBidseparating chamber anda substantially semi-cylindrical damper slidablealong the circumference of said casing to vary the width of saidtangential air inlet.

2. A centrifugal wind classifier as in claim 1 in which said means forvarying the height of the separating chamber comprises means forvertically displacing its upper defining wall.

3. A centrifugal wind classifier as in claim 1, in which said means forfeeding material into said separating chamber comprises a conicalmaterial distributor and a funnel disposed above said materialdistributor to feed material to the outer surface of the materialdistributor and which is adjustable relatively to the materialdistributor to vary the rate of material feed.

4. A centrifugal Wind classifier as in claim 1, also comprising a'platemounted in said separating chamber to References Cited in the file ofthis patent UNITED STATES PATENTS 880,161 Osborne Feb. 25, 19081,761,627 Hine June 3, 1930 2,542,095 Rouget Feb. 20, 1951 2,616,563Hebb Nov. 4, 1952 2,725,983 Rakowsky Dec. 6, 1955

